Image by Flickr user deephoto
The logic here is, if you understand your lens then you will use it better and get more life out of it. Knowing the limitations of your equipment is a big advantage. The object is to help you prevent wear on important components on all of your equipment and it may also help you when it comes time to choose your next lens. Let’s take a look at some integral parts, how they work and the major stress points of zoom lenses.
From a technician’s stand point, those lenses with larger minimum apertures (F2.8 etc.) are generally built better and can withstand more punishment. Furthermore, another indicator of how well the lens is built is whether the lens has a fixed aperture as opposed to a variable aperture (changes as you zoom in and out); those with a fixed are usually built stronger. They have a kind of shell around them and when we work on them they usually need less replacement parts.
Continuing on the subject of aperture, it can and does fail. There are many different ways in which it can fail. Blades can stick, if it’s a power diaphragm it is subject to all the issues electronics can have. One thing users can do to prevent failures is to not zoom unnecessarily. There are a lot of moving parts inside the lens and every time you zoom you are putting wear on them. Rollers, lens elements, possibly a stabilizer and depending on the lens other electronically powered components make up the innards that have moving parts that will eventually wear out.
Zoom lenses are the most popular type of lens. Within them there are two sub-types of zoom lenses; that which zoom internally or telescope out. Internal zoom lenses are usually of the same type that has a fixed aperture. Having fewer internal moving parts and being more or less free from outside “influences” with a protective shell around them is definitely a clear advantage. For capturing light, the bigger the front elements the better; in addition to that if the internal elements stay relatively the same size all the way through the lens it is best. Telescoping lenses typically have a variable aperture. They can have a large front element but may have smaller internal elements which restrict their light gathering capability. Because of the way they are built they also have more parts that move when zoomed.
The major stress point to watch out for on both types of lenses is where the lens mounts to the body (especially if the lens has a plastic mount). Bigger, heavier lenses usually come with a tripod/monopod collar and SHOULD be used; at the very least support with your hand but never just let the lens “hang” off. Another stress point to watch out for is how hard you hit the beginning or end of the zoom. This wears out the connection from the zoom ring to the internal moving parts.
Telescoping zooms have a whole other set of stress points. For starters they will over time develop what is called a “creep” where the lens zooms out on its own when acted upon by gravity (some lenses this is inherent in their design and have a “lock switch”). If you use the lens this will happen over time no matter what you do. You can minimize this effect by not zooming unnecessarily and not hitting the ends too hard. It can be tightened up but only once or twice (depending on the lens) during the life of the lens. Keep in mind, the further out a telescoping zoom is the more stress it puts on the internal pieces it is connected to. This can cause the barrel to become loose and develop a wobble if you put any extra stress or “leave it out” too much.
Both types of lenses have their own drawbacks. The big internal zoom fix aperture lenses are bulky, heavy and very expensive. Telescoping lenses, in general, are less rugged and not as great at gathering light. Remember these are tools and its always best to use the “right” tool for the job.